Bimetallic thermostatic snap switch having adjustable contact bolt



April 26, 1966 J. HUBER 3,248,503 BIMETALLIC THERMOSTATIC SNAP SWITCH HAVING ADJUSTABLE CONTACT BOLT Filed Aug. 12. 1963 INVENTCR 72a Kme Hasi/Q BY /f/@ ATTOR i EY United States Patent() 3,248,503 BIMETALLIC THERMOSTATIC SNAP SWITCH HAVING ADJUSTABLE CONTACT BOLT Jakob Huber, Wurenlos, Switzerland, assignor to J. Huber & Cie. A.G., Wurenios, Switzerland, a corporation of Switzerland l Filed Aug. 12, 1963, Ser. No. 301,283 Claims priority, application 1S/vrtzerland, Mar. 22, 1963,

3,6 3 Claims. (Cl. ZOO-138) The present invention relates to an electric temperatureresponsive switch of very small size, having a bimetallic snap disk, particularly suitable for the control and overload protection of electrical machines and apparatus.

Microswitches of this kind are known which have a circular bimetallic snap-action disk located between two metal plates forming a lenticular casing, whereby, depending on its position, the disk abuts against a contact mounted in one of the casing plates and insulated from the latter, or the disk moves away from saidcontact for opening the switch. Upon heating, the bimetallic disk, which may be curved, bends slowly and separates itself somewhat from the contact before it snaps into a rest position which is determined by the change in temperature. Thi-s slow disengagement results in the formation of an arc which can be prevented in the conventional manner by using a movable contact pin which maintains contact with the disk until the snap action occurs which breaks the contact quickly. In another conventional switch the bimetallic disk is arranged in the casing in a prestressed condition whereby creeping movement of the disk is partly eliminated. This switch has the disadvantage that, if mass-produced, the'temperature at which the snap action occurs in the individual switches is uncertain and can only be subsequently ascertained by means of tests. For this reason, thermostatic switches, which must operate at a definite temperature can be fabricated only '-at a considerable cost and with a great number of rejects.

The object of the invention is to provide a thermostatic switch which `avoids the aforesaid disadvantages of conventional thermostatic switches.

It is an object of the present invention to provide a thermostatic switch, which can be mass-produced and adjusted at minimum cost to respond accurately to predetermined temperatures. There is no slow disconnection of the contacts and arcing is reduced to a minimum.

The microswitch according to the invention comprises a circular bimetallic snap-action disk located between two platelike elements, which together form a lenticular casing. In one of its end positions the disk abuts against a contact bolt screwed into the center of one of said plate elements and is insulated from the latter. The position of the contact bolt is fixed in the respective platelike element and, upon rotation of the bolt, the bolt exerts an adjustable pressure against the middle of the bimetallic disk.

of the invention are set forth with particularity in the appended claims. The invention itself, however, and additional objects and advantages thereof will best be understood from the following description of an embodiment thereof when read in connection with the accompanying drawing, wherein:

FIG. 1 shows an axial section of the switch according to the invention.

FIG. 2 is an axial sectional, large scale illustration of the central part of the switch.

Referring more particularly to FIG. 1 of the drawing, numerals 1 and 2 denote two halves of a lens-shaped casing or housing. The marginal portions of the elements 1 'and 2 are rigidly connected. A bimetallic disk 3 with The novel features which are considered characteristic supervise is reached.

Patented Apr. 26, 1966 Mice snap action is placed inside the casing in the diametrical plane thereof.

As shown in FIG. 2 a contact plate 7, preferablymade of silver, is loosely connected to the center of the bimetallic disk 3. The latter is prestressed by pressing a hollow externally threaded bolt 4 against the plate 7. The bolt 4 is screwed into a flange element 10 which is supported by the element 1 of the casing and is insulated therefrom by-annular insulating elements 11, 12 and 13. Pretension ot the disk 3 depends on the extent the bolt 4 projects into the casing. This pretension is initially adjusted to effect actuation of the switch at a predetermined temperature. After adjustment the position of the bolt 4 may be fixed, for example, by soldering it to the flange 10. A contact element or knob 5, preferably made of silver, is placed inside and concentrically of the bolt or regulating element 4 and is pressed by a spring 6 against the contact plate 7. The element 5 prevents the undesired effect of a residual creeping movement of thebig metal snapping disk 3.

The current liows from a terminal 9' through the elements 10, 4, 5, 6 and 7 and from the latter through a copper conductor 8 to which the plate 7 is rigidly connected and which has au lend portion clamped between the marginal portions of the casing halves 1 and 2. The marginal portion of the casing half 2 is beaded around the marginaly portion of the casing half 1 and the conductor 8 extends into the bead. The conductor 8 conducts the current to ther casing half 1 to which a terminal 9 is connected. The deilection of the disk 3 is limited by the regulating element 4. This limitation is defined by calibrating the switch for the desired response temperature by rotating the4 regulating element after the switch has been Iassembled. Thus it is possible to adjust the response temperature of the switch ,within relatively wide limits. At the same time the additional effect of a comparatively high contact pressure is obtained and the operational capacity of the microswitch is increased. The bimetallic disk requires only a small amount of heat for actuation.

Up to the snapping movement of the bimetal disk 3 the current is conducted ,from the contact plate 7 through the contact knob 5 directly to the bolt 4. This considerably reduces the temperature at which the microswitch is moved to open position and makes the microswitch according to-the invention suitable for use in automatic control apparatus.

Tests have shown that with relatively high currents the bimetallic snap disk is heated directly if current flows therethrough whereby the switching operation occurs before the ambient temperature which the switch has to In order to avoid this, in accordance with the invention, the bimetallic disk 3 is loosely connected to the contact element 7 and a copper strip 8 is firmly attached to the element 7. l With this arrangement the bimetal disk does not conduct any appreciable current and direct heating of the disk 3 due to current flowing therethrough is avoided. The bimetal disk is therefore almost exclusively responsive to the ambient temperature.

Temperature-responsive switches are known wherein silver contacts are riveted or welded to a bimetal disk. This effects the characteristics of the disk in an uncontrollable manner and makes it difficult to manufacture a plurality of switches responding to the same temperature.

The microswitch according to the invention may make contact when in rest position or when in operating position, or both.

If the switch makes contact when in operating position, the element 7 does not abut against the element 5, at normal temperatures. It makes contact only upon an increase'of the temperature of the disk which increase effects the snap action. In this case the switch is suddenly closed, for example, for closing a signal circuit.

If the switch makes contact when in rest position the contact plate 7 abuts against the bolt 4. At rising temperature the disk 3 is slowly bent. Since the disk is pretensioned there is no creeping movement. When the tension of the disk, caused by heating, becomes equal to the pretension produced by the regulating element 4 the disk snaps over to the switch-opening position. The movable contact element 5 must follow the disk 3 only a few hundredth of a millimeter in order to obtain a snapswitch action and eliminate a creeping opening of the switch. Because of the sudden opening of the switch the circuit-breaking capacity of the rather small contact arrangement according to the invention is quite great.

The automatic microswitch according to the invention can deal with alternating Acurrents up to amperes at 220 volts. This is particularly lso if the plate 7 is made so large that it contacts the element 4 in such manner that only a small portion of the current passes through the movable silver contact 5. If a truc snap action is not required, the element 4 may be made, for example, of

silver and the movable contact 5 may be omitted.

I claim:

1. An electric temperature-responsive microswitch comprising:

a substantially lens-shaped housing,

a bimetal snap-action disk disposed inside said housing in the diametrical plane of said housing and connected thereto, and

a contact element screwed to a predetermined extent into Said housing at one end of the central axis thereof for pretensioning said disk to a determined degree,

said disk having two extreme positions and having a central portion abutting against said contact element when in one of said extreme positions,

said contact element being in the form of a hollow bolt,

a contact knob disposed concentrically in the inte-y rior of said hollow bolt, said contact knob having a portion facing said disk and adapted to project from said hollow bolt, and a spring in said hollow bolt urging said knob toward the center of said disk.

2. An electric switch as defined in claim 1, further comprising a contact plate loosely connected to the center of said bimetal disk and adapted to contact said contact element, and an electric conductor rigidly connected to said contact plate.

3. An electric temperature-responsive microswitch comprising:

a substantially lens-shaped housing,

a bimetal snap-action disc place-d inside said housing in the diametrical plane of said housing and connected thereto,

a Contact plate loosely connected to the center of said bimetal disk,

a hollow contact bolt screwed into said housing at one end of the central axis thereof,

said snap-action disk having two extreme positions and said contact plate abutting against said Contact bolt when said disk is in one of said extreme positions,

said contact bolt being screwed to a predetermined extent into said housing for pretensioning said bimetal disk to a predetermined degree,

a contact knob movable inside said contact bolt and having a portion facing said contact plate and adapted to project from said bolt, and

a spring placed inside said contact bolt for urging said knob toward said contact plate.

References Cited by the Examiner UNITED STATES PATENTS 7/ 1956 Mertler 200--138 10/1957 Odenwald 200-138 

1. AN ELECTRIC TEMPERATURE-RESPONSIVE MICROSWITCH COMPRISING: A SUBSTANTIALLY LENS-SHAPED HOUSING, A BIMETAL SNAP-ACTION DISK DISPOSED INSIDE SAID HOUSING IN THE DIAMETRICAL PLANE OF SAID HOUSING AND CONNECTED THERETO, AND A CONTACT ELEMENT SCREWED TO A PREDETERMINED EXTENT INTO SAID HOUSING AT ONE END OF THE CENTRAL AXIS THEREOF FOR PRETENSIONING SAID DISK TO A DETERMINED DEGREE, SAID DISK HAVING TWO EXTREME POSITIONS AND HAVING A CENTRAL PORTION ABUTTING AGAINST SAID CONTACT ELEMENT WHEN IN ONE OF SAID EXTREME POSITIONS, SAID CONTACT ELEMENT BEING IN THE FORM OF A HOLLOW BOLT, 